Two composite membranes were fabricated by incorporating hollow polymer spheres (HPS) with a hydrophilic shell bearing sulfonic (s-HPS) or carboxylic groups (c-HPS) into Nafion polymer matrix using the solution cast approach. The very low specific mass of HPS permits a high volume faction of HPS in the composite membranes on the basis of 0.5 wt % loading. The resulting composite membranes attained a combinatory hydrophilic channel comprising the pendant –SO3H groups of Nafion and hydrophilic HPS with the unperturbed perfluoropolymer phase. This combinatory hydrophilic channel functioned much more effectively than that in the native Nafion membranes in transporting protons, in particular under low humidity conditions or at the medium temperatures (~70–100 °C). This improvement can be attributed to both strong water-retention capability and spherical-surface-sustained proton conduction path. Of the two types of hydrophilic HPS, the s-HPS worked more effectively than the c-HPS in augmenting proton transport on the basis of different water uptake extents and acidities. The influence of temperature (at 100% RH) and humidity (at 20 °C) on proton conduction was investigated to demonstrate the water micro-reservoir role of the two HPS in the composite membranes. Both composite membranes, N/s-HPS and N/c-HPS, offered obviously superior fuel cell performance over the commercial N-112 membrane at 70 °C.
The solution-based method simply allows for impregnation of the graphene oxide network with sulfur nanoparticles through a careful manipulation of pH of the chemical environment.
The proton conductivity of a membrane was measured using the normal four-probe method at different temperatures or under various RH% conditions [,]. The sample cell was composed of two Teflon plates in rectangular shape, on one of which four parallel metal probes were fixed with the two outer ones (stain less steel ribbon) as current-carrying electrodes and the two inner ones (copper wires) as potential-sensing electrodes. In a typical run, a fully hydrated membrane sample was brought in contact with the four electrodes and a window designed on both Teflon plates to allow for rapid equilibrating of the sample with that of the measurement environment. The sample was then immediately placed in a closed chamber with a designated RH% at a selected temperature and the corresponding σ value was recorded down. The electrical resistance of the sample was taken using an electrochemical analyzer (Autolab Instrument) at galvanostatic mode with the AC current amplitude of 0.1 mA and the frequency scanning range from 0.1 Hz to 1 MHz. To evaluate the performance of a membrane in fuel cell, a single cell was operated using pure H2 and O2(1 bar, 50 cm3 min−1) without humidifying hydrogen. The membrane-electrolyte assembly was made by sandwiching the 1M H2SO4-soaked membrane between an anode and a cathode sheet. The anode and cathode sheet were a carbon paper (SGL, Germany) with carbon-supported 20 wt % Pt catalyst layer supplied by E-TEK, Natick, MA. The catalyst loadings at the anode and cathode were 2 mg/cm2, respectively. The effective electrode area was 2 cm2. The electrode polarization curve was obtained by setting a series of cell current and recording the corresponding current voltages.
These hydrophilic HPS aggregates functioned as strong moisture reservoir with prominent effect on proton transport, which will be elaborated in the following section. Despite the positive effect of hydrophilic HPS, a loading exceeding 0.5 wt % would further weaken the cohesive strength of membrane and hence be irrelevant. On the contrary, being hydrophobic in nature, n-HPS particles were likely to be entangled by perfluoro-chains upon drying. As the hydrophobic perfluorocarbon chains take up the major volume fraction and this hydrophobic combination does not or only slightly perturb the ionic clustering of –SO3H throughout the membrane, a dense morphology could still remain after being cryofractured. In summary, the hydrophilic HPS filler acted to broaden proton conducting channel in the composite Nafion membrane.
Subsequently, an interesting and absolutely new application is reported, related to the combination of Radical-Induced Cationic Photopolymerization with Frontal Polymerization, achieving the cross-linking of epoxy composites.
A plausible explanation describing the alignment of pyridine moieties of DHP with the indene side groups of IC60BA is presented with a view to improving the performance of the BHJ PSCs via improved crystalline order and hydrophobicity changes.
This paper aims to review the background biological knowledge of human tactile sensing, to give an understanding of how we sense and interact with the world through the sense of touch, as well as the conventional and state-of-the-art technologies of tactile actuators for tactile feedback delivery.
The analysis results provide the explanation of the experimental results that the Nomex/TPU system has the greatest potential for producing helical nanofibers, while the PS/TPU and PAN/TPU systems cannot fabricate helical fibers effectively.
The improved device performance is attributed to the enhancement of charge carrier mobility leading to a decreased charge carrier recombination and improved charge collection efficiency.
Following the examination on the water uptake under various RH% (), the three membranes revealed different rising trends of proton conductivity with the increase in temperature from 20 to 90 °C under constant 10% RH (a). In such a chamber, the membranes captured just 6–9 wt % water at 20 °C and the bulk moisture levels would be lower than this range at higher temperatures. This test demonstrated the impact of the bound acid groups as well as the structure of hydrophilic channel on transport of protons because the Grotthuss mechanism became subsidiary at such moisture level. The conductivity values though show the order of magnitude of −3 under 10% RH, the discrepancies of them tell the capability of shipping protons by pendant acid groups, –SO3H and –CO2H. The N/s-HPS membrane presented the strongest capability of shipping protons through contact of spherical surface () because this two-dimensional mould is far more efficient than transport along tangled polymer chains. A similar test was conducted to collate the proton-conductivity decreasing profile with the measurement time under 10% RH and at 20 °C (b).
The results suggest that there are certain hybrid composite combinations that could lead to the development of highly multifunctional composites with better strength, stiffness, damping and electrical conductivity.
In this article, the authors have briefly introduced their recent studies on the utilization of nitrogen-doped activated carbon (N-AC) for several organic synthesis reactions, which include base catalyzed reactions of Knoevenagel condensation and transesterification, aerobic oxidation of xanthene and alcohols, and transfer hydrogenation of nitrobenzene, 3-nitrostyrene, styrene, and phenylacetylene with hydrazine.
About 0.2 g SiO2-MPS powder was dispersed into 80 mL of acetonitrile under ultrasonication in a 100 mL flask, equipped with a fractionation column, a condenser, and a receiver. A mixture of St (1.15 mL, 0.01 mol), DVB (0.267 mL, 0.0015 mol, 15 mol% relative to styrene), and 2,2'-azobisisobutyronitrile (AIBN, 0.02 g) was then added into the flask. The polymerization then proceeded under reflux and removing of solvent by gradual distillation. Through this distillation process, the P(St-DVB) network formed in the solution phase underwent effective grafting to the MPS surface anchors, leading to a polymer shell on each SiO2 microsphere. The reflux lasted 1.5 h and 40 mL acetonitrile was distilled off. The resultant SiO2-P(St-DVB) core-shell microspheres were purified using soxhlet extraction procedure in which the remaining monomers and oligomers were removed by a binary solvent of acetonitrile and ethanol. The resulting SiO2-P(St-DVB) powder was vacuum dried at 50 °C. The particles were then sulfonated in a concentrated sulfuric acid at 50 °C for 3 h and the mixture was poured into a cold ethanol to allow sedimentation of pale yellow particles. After centrifuging and washing with ethanol, the collected powder was vacuum dried. Similarly, the preparation of SiO2/P(MAA-DVB) was prepared by the distillation polymerization except sulfonation. Hence two different types of hydrophilic SiO2/polymer core-shell particles were synthesized.